Jupiter.

Due to Moon's late night affair with Jupiter, she became pregnant with their child. When Moon told his parents, they were were surprised, while Sun scoffed at the thought. Even though Moon's relationship with his sister had diminished, he had found new found love with Jupiter, who later gave birth their young baby boy, Mars. Who took after Moon in almost every way.

After gradating from college, Moon took up her dream job of being a cook. While Jupiter fulfilled her dream of writing a novel.
Later they moved in with one another, Jupiter taking up the role of being a stay-at-home mom, while Moon made most of their income as master chef at a well-known restaurant.

They continued to love each other even after their grandchildren had been born. Living happy lives together.